Influenza and its secondary pneumonias are the fourth leading cause of death in persons 65 years and older in the United States. Caloric restriction (CR) extends median and maximal life span in healthy rodents, compared to those fed ad-libitum (AL). Aged CR rodents show decreases in tumors and cancers, and increases in antibody titers and T cell proliferation suggesting CR delays the onset of age-related decreased immune function. We have employed a mouse model of CR to examine the age-related decline in primary response to influenza. Although CR delayed the age-related decline in T cell proliferation, in stark contrast, aged CR mice died 4-6 days after primary influenza infection, exhibiting increased lung virus titers and reduced pulmonary NK activity. Importantly, CR mice weighed 30% less than AL mice at the time of infection and had dramatic weight loss following infection. Due to the early time course, we hypothesize that aged CR mice cannot control primary influenza infection because of altered innate immunity. This may reflect an intrinsic defect in NK cells themselves or may be secondary to an extrinsic defect involving signals produced early on by macrophages and/or dendritic cells. Specifically, we will: 1) Determine if enhanced susceptibility of CR mice to primary influenza infection is age-dependent. Young AL and CR C57BL/6 mice will be infected with influenza and survival, weight loss and recovery, cell types in lung and mediastinal lymph nodes, and lung virus titers will be evaluated. 2) Investigate mechanism(s) for reduced NK activity during primary influenza infection. We will assess NK function by cytotoxicity, perforin and granzyme production, in vitro stimulation of NK cells with IFN-a/[unreadable], and cytokine production. We will investigate whether decreased NK cell activity is related to decreased NK cell number or NK cells as a percentage of total lymphocytes in lung. We will further determine if the defect in NK number or function results from impaired recruitment and/or activation of NK cells by cytokines produced by macrophages/dendritic cells. We will quantitate activation markers on macrophage and dendritic cells in lung and their cytokine and chemokine production (IFN-a/[unreadable]?, IL-12, IL-15, IL-18, MIP-1a/[unreadable], MCP-1, IL-1[unreadable], IL-6, TNF-a). 3) Determine if the susceptibility of CR mice to influenza is related to reduced body weight and if refeeding prior to infection restores the immune response to influenza infection. CR mice will be fed AL diets to restore weight to 50% and 100% of AL mice before infection with influenza and outcomes in Specific Aims 1 and 2 will be assessed. [unreadable] [unreadable] [unreadable]